Suggest a book that affects you as much as Flowers for Algernon

I read Flowers for Algernon recently and I’m still thinking about it. The way it makes you feel Charlie’s decline just through the writing itself is unlike anything I’ve experienced in a book. I finished it feeling genuinely bereft.

Looking for something that hits in a similar way. Not necessarily the same subject matter, just that same quality of leaving you hollowed out and changed. Any genre welcome. Thanks!